The term “submarining” means the slipping forward of a vehicle occupant under the seat belt in an impact situation such as a vehicle crash in case the lap belt fails to restrain the pelvis of the vehicle occupant. This occurs most frequently when the vehicle occupant is sitting on an edge of the seat and/or the seat back is significantly reclined, and could impair the restraining capability of the seat belt because the seat belt fails to restrain the proper part of the vehicle occupant.
A copending U.S. patent application Ser. No. 09/526,405 filed Mar. 15, 2000 discloses a vehicle occupant restraint system in which a forward slip preventing member is moveably supported by a pair of casings fixedly attached to either side of a seat frame at a front part of a seat bottom so as to selectively project upward. The front end of the seat is raised only in case of an impact situation such a vehicle crash by actuating this forward slip preventing member with a power unit. The contents of this copending application are hereby incorporated in this application by reference.
The front end of the seat or the cushion member of the seat cushion which is raised by the forward slip preventing member is almost entirely crushed by the load of the vehicle occupant in the impact situation, and the forward slip preventing member practically directly engages the legs of the vehicle occupant. This could cause some discomfort to the vehicle occupant, and a measure to reduce the impact is desired.
For instance, a part or all of the cushion member may be formed with an energy absorbing material made of foamed resin or the like which provides a favorable energy absorbing property, but this not only increases the cost but also impairs the ride quality for the vehicle occupant as compared to the more conventional seat made solely of common cushion material.